Vortex Shedding in Confined Swirling Flow of Polymer Solutions

Abstract

A ring vortex shedding phenomenon observed in the confined swirling flows of polyacrylamide (PAA) solutions whose concentrations were 0.5wt% and 1.0wt% was investigated using particle image velocimetry (PIV) system. It was found that the fluid within the ring vortex formed near the rotating disc rorates with semi-rigid rotation, where the angular velocity of ring votex was about 0.9times that of the rotating disc. The high shear layer was found to exist at the boundary between the ring vortex and the outer large-scale secondary flow. After the ring vortex was shed, the surrounding large-scale secondary flow moved into near the rotating axis, so that the strong axial flow was observed near the rotating axis. Periodic azimuthal and radial velocity fluctuations with considerably large amplitude, in which their correlation varied with the radial locations, were seen for the nonaxisymmetric ring vortex which was observed for the higher Reynolds number compared to that of the axisymmetric ring vortex.